Human immunodeficiency virus (HIV) infection causes the acquired immunodeficiency syndrome (commonly known as AIDS). HIV is a retrovirus that primarily infects T cells expressing the CD4 glycoprotein, i.e., CD4+ T-cells, which are also known as helper T-cells. HIV virus multiplies in helper T-cells and destroys the host helper T-cells, resulting in cellular immunity depression and leaving the infected patient susceptible to opportunistic infections, malignancies and various other pathological conditions. Ultimately, HIV infection can cause depletion of helper T-cells and collapse of a patient's immune defenses. Not surprisingly, HIV-infected individuals and AIDS patients typically develop AIDS-related conditions such as AIDS-related complex (ARC), progressive generalized lymphadenopathy (PGL), dementia, tropical paraparesis, Kaposi's sarcoma, thrombocytopenia purpurea, herpes infection, cytomegalovirus infection, Epstein-Barr virus related lymphomas among others. In any case, the HIV viruses in an infected individual are infectious and can be transmitted to other people through blood transfusion or sexual contacts.
Efforts have been made in the past fifteen years or so in developing vaccines for treating or preventing HIV infection and AIDS. Various forms of vaccines have been proposed and tested in animal models or humans. These include whole killed and live-attenuated HIV viruses, recombinant viral particles, recombinant viral or bacterial vectors capable of expressing antigenic HIV proteins, recombinant HIV proteins, and DNA vaccines. However, none has successfully passed clinical testing.
There has also been a great deal of effort in developing pharmaceutical compounds for treating HIV infection and AIDS. The therapeutic approaches have been mostly focused on a limited number of drug targets, namely HIV reverse transcriptase, HIV protease, and HIV integrase. A number of reverse transcriptase inhibitors and protease inhibitors have been developed or marketed. Examples of nucleoside reverse transcriptase inhibitors include Zidovudine, Stavudine, Lamivudine, and ddI. Examples of non-nucleoside reverse transcriptase inhibitors include Efavirenz, Delavirdine, and Abacavir. In addition, a number of HIV protease inhibitors are commercially available including Ritonavir, Nelfinavir, Indinavir and Saquinavir.
However, HIV typically undergoes active mutations as it multiplies. In addition, there are extensive genetic variations in HIV partly due to high mutation rate. Therefore, mutations in HIV reverse transcriptase and protease arise frequently in infected individuals and render the virus resistant to the inhibitor administered to the individuals. Combination therapy, generally referred to as HAART (highly active anti-retroviral therapy), has been developed in which a combination of different anti-HIV inhibitors is administered to a patient. However, viral resistance to combination therapies still frequently develops. In addition, many of the anti-HIV compounds known in the art have other serious drawbacks. For example, the reverse transcriptase inhibitors such as AZT and ddI are fairly toxic and cause serious side effects in patients treated with such compounds.
Therefore, although limited success for controlling HIV infection and AIDS has been achieved with previously developed anti-HIV compounds, there is a need for alternative therapeutic and prophylactic methods that overcome the shortcomings of currently available approaches.